Re: When to call it?
We operate a small mobile stage. It's roughly 24ft x 12ft so dwarfed by many of the other structures under discussion here, but is big enough to require inspection.
In the UK the local council is responsible for inspection of the structure. If the overall height from the ground exceeds 12ft or the platform height exceeds 2ft then an inspection is mandatory. We have operated the stage for two seasons now. Inspections have ranged from a serious, in-depth look, to a cursory glance and a tick in a box. Even if they don't go through every detail with our stage, the inspectors would be a lot more thorough with something that looks homebrewed or they haven't seen before.
Our own stage is a custom-built unit, and since the manufacturer didn't have any certification for a one-off construction we ended up getting a test done ourselves to satisfy the first council we came across. (This entailed loading weights onto the stage with a forklift and checking for deflection in the structure). The council officer did his own calculations to work out a maximum wind speed that he was happy with.
A friend of mine worked a gig where a truck stage was supplied. Council inspector was (justifiably) unhappy with the load capacity, and insisted that the company added more bracing underneath, and also stipulated that they had to retighten some of their supports every hour, on the hour, since he suspected that they could work loose. And it was made very clear to them that their stage would not be allowed to be erected in the city again without quite substantial modification.
I would expect that a structure the size of the one which failed in Indianna would have been gone over with a fine tooth comb if it were erected in the UK. (Plans would be scrutinised beforehand and the final structure inspected to ensure it matches the design). The potential problems that have been alleged (missing ballast, lack of cross bracing) would have been spotted and if not rectified the council will pull the event licence.
However, there are still gaps. I suspect plenty people put structures up and just don't bother telling the council. Outside of a city centre or major festival, it's unlikely that anyone would get "caught". Some of the worst structures I've been around have been put up on private ground and there is nobody policing them. But I'm not sure how the local festival market can be made safer without employing an army of inspectors, especially outside of metropolitan areas where it simply isn't possible to get an inspector round more than a handful of events in one day.
Perhaps the biggest positive effect of the disaster in Indianna will be raising the public's awareness of the importance of structural safety. If the coverage of the stage falling makes bands think twice about what they are playing under, or inspires someone on a local festival's organising committee to have a closer look at what the lowest bidder is going to assemble for them, that can only be a good thing.
